1. Field of the Invention
The invention relates to an overvoltage protection system for diverting transient overvoltage with two electrodes, each of which has one current terminal, an air-breakdown spark gap which acts between the electrodes, and a housing which holds the electrodes.
2. Description of Related Art
Electrical, but especially electronic measurement, control and switching circuits, mainly also telecommunications means and systems, are sensitive to transient overvoltage, as can occur especially as a result of atmospheric discharges, i.e., by lightning stroke currents, but also due to short circuits and switching operations in power supply networks. This sensitivity has increased to the degree to which electronic components, especially transistors and thirsters, are used; mainly, the integrated circuits which have been increasingly used are greatly endangered by transient overvoltage.
In addition to the overvoltage protection element underlying the invention (see, German Patent No. DE 37 16 997 C2), i.e., one with an air-breakdown spark gap, there are overvoltage protection elements with an air-spark over spark gap in which a creeping discharge occurs upon triggering (compare, published German Patent Applications DE 27 18 188 A1, DE 29 34 236 A and DE 31 01 354 A1).
Overvoltage protection elements of the type underlying the invention, i.e, those with an air-breakdown spark gap, compared to overvoltage protection elements with an air-spark over spark gap, have the advantage of higher surge current carrying capacity, but the disadvantage of a higher and also not especially constant operating voltage.
Various overvoltage protection elements with an air-breakdown spark gap have been developed which have also been improved with respect to the operating voltage (compare DE 41 41 681 A1, DE 41 41 682 A1, DE 42 44 051 A1 and DE 44 02 615 A1, the last mentioned German Patent corresponding to U.S. Pat. No. 5,604,400).
The overvoltage protection element known from U.S. Pat. No. 5,604,400 has already acquired great importance in practice, is produced and sold by the assignee of the present application under the name FLASH TRAP FELT (see, ""98/99 catalog of the company Phoenix Contact GmbH and Co, Bloomer, Germany, Parts Catalog 7 xe2x80x9cTRABTECH Overvoltage protectionxe2x80x9d and the explanations given there on the problem of overvoltage, especially on pages 3-5 and 12-17). In this known overvoltage protection element, each electrode has a terminal leg and an arcing horn which runs at an acute angle to the terminal leg, and the arcing horns of the two spaced electrodes together form the air-breakdown spark gap. Here, between the opposite ends of the terminal legs of the two electrodes, there is an ignition aid which triggers a creeping discharge. In addition, it can be obtained from U.S. Pat. No. 5,604,400 that it is advantageous if the arcing horns of the electrodes are provided with a hole in their areas which border the terminal leg.
The above addressed overvoltage protection element, which is known from U.S. Pat. No. 5,604,400, is made in a practical implementation such that, on the one hand, it has a surge current carrying capacity of 100 kA, and on the other hand, it is suitable for extinguishing network follow currents into the range of 100 A.
The primary object of the present invention is to provide another overvoltage protection element with an air-breakdown spark gap which, with reference to the operating voltage, the lightning surge current and the network follow current carrying capacity behavior and the network follow current extinguishing behavior meets current requirements in a special way.
The overvoltage protection element as in accordance with the present invention is, first of all, essentially characterized in that the electrodes are located parallel to one another. In this case, the electrodes can be made cylindrical and can have a circular, oval and/or a rectangular cross section. It is especially advantageous if the electrodes have different cross sections over their length. Different cross sections means not only a difference in geometry, therefore circular, oval or rectangular, but also in dimensions; therefore, the electrodes can be staggered (stepped) in cross section along their length, so that the area which is to act as the air-breakdown spark gap can be locally set in a special way.
It is especially advantageous for the serviceability of the overvoltage protection element in accordance with the present invention if the interior of the housing which holds the electrodes is lined, the lining being made, preferably, of POM Teflon(copyright).
In the prior art, especially also in the overvoltage protection element which is disclosed by U.S. Pat. No. 5,604,400, in cross section, the air-breakdown spark gaps are generally designed as extinguishing spark gaps. Conversely, another teaching of the invention which acquires special importance is that, in the overvoltage protection element in accordance with the invention, the housing which holds the electrodes is closed and pressure resistant.